1. Field of the Invention
The invention relates to a method for manufacturing a hollow object, such as an article footwear, a helmet, a bag, a sports accessory, or the like, the object including synthetic materials. The invention also relates to a product containing the object obtained by the method.
2. Description of the Background
Conventionally, hollow objects, such as footwear, are manufactured by combining an upper and a sole assembly. The upper generally includes a number of parts, such as a lateral quarter, a medial quarter, a vamp, a tongue, a heel, a rear counter, a protective toe-cap, a tightening device including keepers and a lace, an inner lining, and may even include additional parts. Moreover, some of these parts may include a plurality of portions. The main problem in a traditional shoe is in assembling and turning parts that are cut and flat assembled into a three-dimensional shape. Conventionally, the upper is associated with a lasting sole to demarcate a footwear element. According to a first method, the upper is bonded to the lasting sole using an adhesive layer. The lasting sole, also referred to as the lasting board, is relatively rigid to withstand the lasting process. The bonding operation is carried out by pulling the upper and pressing it flat onto the lasting board, with a last positioned in the upper. This is the traditional shoe lasting assembly. This technique makes it possible to exert sufficient pressure when heating the adhesive in order to produce the footwear element. A second method, also known, involves producing the footwear element by stitching the upper to the lasting board. This is referred to as the Strobel assembly. The lasting board in this case is a flexible stitchable sole, referred to as the Strobel sole. For each of the first and second methods, the lasting board is integral with the sole assembly. The sole assembly further comprises external parts, such as one or more damping layers and a wear layer adapted to contact the ground, which are generally attached with an adhesive to the lasted board and upper. The sole assembly further comprises one or more inner layers arranged in the footwear element to fulfill protective functions in terms of hygiene, shock absorption, arch support, or the like. In the end, the association of the footwear element with the other constituent parts of the sole assembly forms the shoe.
Irrespective of the method used for its manufacture, a traditional shoe has certain drawbacks. First, the shoe uses a large number of parts, typically between forty and sixty parts. Such a large number of shoe-forming parts increases the number of manufacturing operations and the time required to carry out such operations. It usually takes forty minutes to one hour and thirty minutes to make a shoe. It can be said that the shoes made using conventional techniques are complicated, both by the number of their components and the number of manufacturing operations.
Another disadvantage results from the structural discontinuity of the shoe, in particular in the area of the upper. For example, a part of reduced size, superimposed on another, larger part, may sometimes considerably modify the bendability of the upper in the location of the small part. This may sometimes hinder a user and makes the shaping of the shoe, that is, the three-dimensional shaping, more difficult.
A further disadvantage is due to the presence of free spaces between the foot and the shoe. This means that the foot is not in contact with the upper or the sole assembly in certain areas. This is especially true in the area of certain portions of the junction between the upper and the lasting board. As a result, undesired displacements occur sometimes between the foot and the shoe, which can cause discomfort or injuries.
Finally, it can be said that a traditional shoe does not always ensure support and/or adequate tightening of the foot, or does not always provide satisfactory comfort for the foot. Moreover, this shoe does not systematically conform to all foot deformations.
In view of the foregoing, a development has been to provide an improved article of footwear. The latter, according to the noted development, comprises a first shell, the first shell extending lengthwise from a rear end to a front end, widthwise between a lateral side and a medial side, and height-wise from a base to an upper end, the first shell including threads linked to one another mechanically, at least some of the threads comprising at least one hot-melt filament. The threads comprising at least one hot-melt filament are distributed over the entire first shell, and the shape of the first shell is set by melting the threads comprising at least one hot-melt filament.
As a consequence of this arrangement, the first shell can be shaped to have a geometry that is very similar to that of a foot and thereby conforms to the foot in a very uniform fashion. This means that the foot is in contact, or at least very close to, the first shell. This results in an evenly distributed support of the foot, and very few undesired displacements, or even no displacements, between the foot and the first shell. A resulting advantage is increased comfort of the article of footwear produced by the development, compared to a traditional shoe.
Another consequence of the arrangement according to the development is that the first shell has structural continuity, in the sense that its inner surface and/or outer surface are substantially uniform. Physical properties of the first shell, such as bending, for example, may vary depending on zones of the shell. This results in less discomfort for the user.
A synthesis of the foregoing shows that the first shell supports the foot and provides adequate comfort therefor. Furthermore, the first shell is capable of conforming to the foot deformations. This enables the article of footwear to fit comfortably in any situation, be it a static or dynamic situation.
A further consequence of the development is the reduced number of parts for manufacturing the article of footwear, although it may be provided with a few additional parts. The first shell in itself is a minimalist assembly compared to a traditional footwear element. The first shell from the development is a unitary element which, by itself, replaces at least the lateral and medial quarters, a vamp, a tongue, a rear counter, a lasting board, or even more parts. As a corollary, the development considerably reduces the number of manufacturing operations and the time required to carry them out. It generally takes less than thirty minutes to produce a shoe according to the development. The resulting advantage is that the article footwear is much simpler, in any sense, than a traditional shoe. The structural simplicity of the development does not reduce the number of technical functions performed by the article of footwear, compared to a traditional shoe. Paradoxically, one can even say that the structure simplicity is a source of technical improvements in terms of quality and quantity.
Nevertheless, it has been observed that disadvantages remain, despite these improvements. This is the case with respect to quality, for example, which is still insufficient. This means that for the above-mentioned development, the first shell sometimes has manufacturing defects. An example of a defect is unevenness in the fusion of the threads, which results in one or more localized alterations of the physical or mechanical properties of the shell. In this case, the shell locally has different properties than those desired. Without limitation, it may be elasticity, porosity, resistance to wear, or the like. Another example of defect is a localized alteration of the shape or appearance. This is particularly the case if the shell is locally pleated. This is essentially a cosmetic but annoying defect in the sense that it prevents the sale of the product.